Disclosed are: an antibody against a human IL-3Rα chain, which does not inhibit an IL-3 signal, can bind to a B domain of the human IL-3Rα chain, and cannot bind to a C domain of the human IL-3Rα chain； a composition for preventing or treating a blood tumor in which IL-3Rα-expressing cells are observed in a bone marrow or a peripheral blood in a subject, which is characterized by comprising the human IL-3Rα antibody as an active ingredient； and a method for treating a blood tumor in which IL-3Rα-expressing cells are observed in a bone marrow or a peripheral blood, which is characterized by administering a composition containing the human IL-3Rα antibody as an active ingredient to a subject.
